1. Field of the Invention
The present invention relates to a scroll-type compressor, and more particularly to a scroll-type compressor provided with an eccentricity adjusting bushing having an inner opening, and a driving pin inserted into the opening, said opening and driving pin each provided with a stopper which is capable of limiting the rotation of the bushing with respect to the driving pin by virtue of mutual interference thereof, thereby limiting a change of radius of the orbital movement of an orbiting scroll within a desired minute range.
2. Description of the Prior Art
Conventionally, a known scroll-type compressor comprises, as described in FIG. 4, a stationary scroll 10 provided thereunder with an involute or spiral-shaped wrap 10a and an orbiting scroll 11 provided thereon with a wrap 11a of the same shape as that of the wrap 10a but having a rotated orientation, said wraps 10a and 11a engaging with each other in order to provide a compression chamber 5 therebetween. The compressor also includes a driving shaft 1 connecting the orbiting scroll 11 to a motor 12 in order to transmit a driving power from the motor 12 to the scroll 11, thereby causing the scroll 11 to orbit.
In FIG. 4, the reference numeral 13 denotes an airtight case for enclosing the above parts therein.
In operation, upon driving the motor 12, the orbiting scroll 11 rotates by virtue of the driving power having been transmitted from the motor 12 by way of the driving shaft 1 so that the wrap 11a of the orbiting scroll 11 orbits continuously about the axis of the wrap 10a of the stationary scroll 10 without changing the attitude thereof with respect to the wrap 10a, thus the volume of the compression chamber 5 is periodically reduced. Accordingly, a fluid, for example a gaseous refrigerant taken into the compression chamber 5 through a gas intake port 6 and a suction chamber 7, is compressed, then fed to a discharge chamber 8 formed in the center portion of the wrap 11a of the stationary scroll 10, and finally discharged through a discharge hole 8a formed in the stationary scroll 10.
At this time, the distance between respective centers of the involute spirals of the wraps 10a and 11a of respective scrolls 10 and 11, that is, the crank radius, is maintained constant in the orbital movement of the orbiting scroll 11.
In addition, the known compressor generally needs to be provided with an eccentricity adjusting bushing for preventing a leakage of the compressed refrigerant gas through two types of clearances generally formed between the wraps 10 and 11. One leak path is axial clearance formed between outermost ends 9 of each wrap 10, 11 and bottom surface 14 of opposite wrap 11, 10 and the other leak path is the radial clearance formed between facing side surfaces of the wraps 10a and 11a. The eccentricity adjusting bushing is capable of sealing the compression chamber 5 taking account of a counter pressure, thereby preventing a gas leakage in a radial direction. The eccentricity adjusting bushing is rotatably mounted in a hollow shaft downwardly and integrally formed with the orbiting scroll 11.
U.S. Pat. Nos. 4,585,402 and 4,585,403, both published on Apr. 29, 1986, each discloses a representative example of the scroll-type compressor with the above eccentricity adjusting bushing.
As described in FIGS. 2 and 3 showing the construction of the eccentricity adjusting bushing of the scroll-type compressor disclosed in the U.S. patent, the bushing 3 has a cylindrical shape having an inner cylindrical opening 3a eccentrically formed therethrough. Thus, the wall thickness of the bushing 3 is not uniform. The bushing 3 is inserted into a cylindrical opening of a downwardly extending shaft 11b of the orbiting scroll 11 and rotatably receives a driving pin 2 integrally formed with an upper end of the driving shaft 1.
In the operation of the compressor thus constructed, the compression of refrigerant gas is performed in accordance with the orbital movement of the orbiting scroll 11. At this time, a load arising due to gas compression is transmitted from the shaft 11b of the orbiting scroll 11 to the eccentricity adjusting bushing 3, with the loading conditions being as shown in FIG. 3. As shown in the FIG. 3, the load includes two components, one being a radial load, mainly the centrifugal load Fc of the orbiting scroll 11, and the other being a gas compression load Fg, that is, a total reaction load imposing on the wrap 11a of the orbiting scroll 11 according to the gas compression, said gas compression load Fg acting on the bushing 3 in a direction at an angle to the acting direction of the radial load Fc.
These load components Fc and Fg act on a center point O.sub.3 of the eccentric bushing 3, said point O.sub.3 being identified with a center of the orbiting scroll 11. As shown in FIG. 3, these load components Fc and Fg and a resultant load F (=Fc+Fg) act on the center point O.sub.3 of the bushing 3 when the orbiting scroll 11 orbits in a clockwise direction.
Here, the eccentricity adjusting bushing 3 rotatably receives, as described above, the driving pin 2 of the driving shaft 1 by means of its opening 3a so that the bushing 3 eccentrically rotates on a center point O.sub.2 of the driving pin 2, said point O.sub.2 being spaced apart from the center point O.sub.3 of the bushing 3 in a distance "e". Thus, the resultant load F is capable of producing a moment M about the center point O.sub.2 of the pin 2, said moment M being imposed on the bushing 3 and given by: EQU M=F'.times.e
where, the load F' is a divided load of the resultant load F.
Here, the orbiting scroll 11 is engaging with the bushing 3, thus the moment M about the point O.sub.2 also acts on the orbiting scroll 11. In result, the moment M acting on the orbiting scroll 11 is capable of producing a force which is capable of radially urging the wrap 11a of the orbiting scroll 11 toward the wrap 10a of the stationary scroll 10. The urging force is capable of accomplishing the sealing of the compression chamber 5, thereby preventing the above-mentioned radial leakage of the compressed refrigerant gas inside the compression chamber 5 through the radial clearance between the scrolls 10 and 11.
However in the above eccentricity adjusting bushing structure, the sealing effect which is capable of preventing the radial leakage of the compressed gas by virtue of the moment M is considerably influenced by a positional relation between the respective center points, that is, a center point O.sub.1 of the driving shaft 1, the center point O.sub.2 of the driving pin 2 and the center point O.sub.3 (=the center point of the orbiting scroll 11) of the eccentric bushing 3. Hence, the known scroll-type compressor with an eccentricity adjusting bushing has a disadvantage in that it can not limit an excessive eccentric rotation of the eccentricity adjusting bushing on the center point of the driving pin, thereby causing a radius of orbital movement, that is, the distance between the respective centers of the driving shaft and the bushing, said radius of orbital movement being known as an important factor considerably influencing on the compressing effect of the compressor, to excessively change due to the cylindrical structure of the bushing and the driving pin.